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        <p>Library Version 12.1.6.2</p>
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          <td width="20%" align="left"><a accesskey="p" href="txnapp.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 2. Transactional Application</th>
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    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="simpleprogramlisting"></a>Program Listing</h2>
          </div>
        </div>
      </div>
      <div class="toc">
        <dl>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#repconfiginfo_cxx">
                            
                            <span>Class: RepConfig</span>
                    </a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#simpletxnusage_java">Class: SimpleTxn</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#simpletxnmain_java">Method: SimpleTxn.main()</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#simpletxn_init_java">Method: SimpleTxn.init()</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#doloop_java">Method: SimpleTxn.doloop()</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#printstocks_c">
                            
                            
                            <span>Method: SimpleTxn.printStocks()</span>
                    </a>
            </span>
          </dt>
        </dl>
      </div>
      <p>
                Our example program is a fairly simple transactional
                application. At this early stage of its development, the
                application contains no hint that it must be network-aware
                so the only command line argument that it takes is one that
                allows us to specify the environment home directory.
                (Eventually, we will specify things like host names and
                ports from the command line).
            </p>
      <p>
                Note that the application performs all writes under the
                protection of a transaction; however, multiple database
                operations are not performed per transaction. Consequently,
                we simplify things a bit by using autocommit for our 
                database writes.
            </p>
      <p>
                Also, this application is single-threaded. It is possible
                to write a multi-threaded or multi-process application that 
                performs replication. That said, the concepts described in
                this book are applicable to both single threaded and
                multi-threaded applications so nothing
                is gained by multi-threading this application other than
                distracting complexity. This manual
                does, however, identify where care must be taken when
                performing replication with a non-single threaded
                application.
            </p>
      <p>
                Finally, remember that transaction processing is not described in
                this manual. Rather, see the 
                <em class="citetitle">Berkeley DB Getting Started with Transaction Processing</em> guide for details on 
                that topic.
            </p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="repconfiginfo_cxx"></a>
                            
                            <span>Class: RepConfig</span>
                    </h3>
            </div>
          </div>
        </div>
        <p>
                            Before we begin, we present a 
                            class that we will use to maintain useful
                            information for us. Under normal circumstances,
                            this class would not be necessary for a simple
                            transactional example such as this. However, this code will
                            grow into a replicated example that needs to
                            track a lot more information for the
                            application, and so we lay the groundwork for
                            it here.
                    </p>
        <p>
                            The class that we create is called
                            
                            <code class="classname">RepConfig</code>
                            and its only purpose at this time is to track
                            the location of our environment home directory.
                    </p>
        <pre class="programlisting">package db.repquote_gsg;

public class RepConfig
{
    // Constant values used in the RepQuote application.
    public static final String progname = "SimpleTxn";
    public static final int CACHESIZE = 10 * 1024 * 1024;

    // member variables containing configuration information
    public String home; // String specifying the home directory for 
                        // rep files.

    public RepConfig()
    {
        home = "TESTDIR";
    }

    public java.io.File getHome()
    {
        return new java.io.File(home);
    }

}  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="simpletxnusage_java"></a>Class: SimpleTxn</h3>
            </div>
          </div>
        </div>
        <p>
                            Our transactional example will 
                            consist of a class,
                            <code class="classname">SimpleTxn</code>, that performs
                            all our work for us. 
                    </p>
        <p>
                            First, we provide the package declaration and
                            then a few import statements that the class
                            needs.
                    </p>
        <pre class="programlisting">package db.repquote_gsg;

import java.io.FileNotFoundException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

import com.sleepycat.db.Cursor;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.DatabaseType;
import com.sleepycat.db.Environment;
import com.sleepycat.db.EnvironmentConfig;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;
import db.repquote_gsg.SimpleConfig;

public class SimpleTxn
{
    private SimpleConfig simpleConfig;
    private Environment dbenv; </pre>
        <p>
        Next, we provide our class constructor. This simply initializes our
        class data members.
</p>
        <pre class="programlisting">    public SimpleTxn()
        throws DatabaseException
    {
        simpleConfig = null;
        dbenv = null;
    }  </pre>
        <p>
        And then we provide our <code class="methodname">usage()</code> method. At
        this point, this method has very little to report:
</p>
        <pre class="programlisting">    public static void usage()
    {
        System.err.println("usage: " + simpleConfig.progname);
        System.err.println("-h home");

        System.exit(1);
    }  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="simpletxnmain_java"></a>Method: SimpleTxn.main()</h3>
            </div>
          </div>
        </div>
        <p>
                            Having implemented our
                            <code class="methodname">usage()</code>
                            method, we can jump directly into our
                            <code class="methodname">main()</code>
                            method. This method begins by instantiating a
                            <code class="classname">RepConfig</code> object, and
                            then collecting the command line arguments so
                            that it can populate the object with the
                            appropriate data (just the environment home
                            directory, at this time):
                    </p>
        <pre class="programlisting">    public static void main(String[] argv)
        throws Exception
    {
        SimpleConfig config = new SimpleConfig();
        // Extract the command line parameters
        for (int i = 0; i &lt; argv.length; i++)
        {
            if (argv[i].compareTo("-h") == 0) {
                // home - a string arg.
                i++;
                config.home = argv[i];
            } else {
                System.err.println("Unrecognized option: " + argv[i]);
                usage();
            }
        }  </pre>
        <p>
        And then perform a little sanity checking on the command line
        input:
</p>
        <pre class="programlisting">        // Error check command line.
        if (config.home.length() == 0)
            usage();  </pre>
        <p>
            Now we perform the class' work. To begin, we initialize the
            object. The <code class="methodname">init()</code> method actually
            opens our environment for us (shown in the next section).
    </p>
        <pre class="programlisting">        SimpleTxn runner = null;
        try {
            runner = new SimpleTxn();
            runner.init(config);  </pre>
        <p>
            And then we call our <code class="methodname">doloop()</code>
            method. This method is where we perform all our database
            activity. See <a class="xref" href="simpleprogramlisting.html#doloop_java" title="Method: SimpleTxn.doloop()">Method: SimpleTxn.doloop()</a>
            for it's details.
    </p>
        <pre class="programlisting">                    runner.doloop();  </pre>
        <p>
            And then, finally terminate the application (which closes our
            environment handle) and end the method.
    </p>
        <pre class="programlisting">            runner.terminate();
        } catch (DatabaseException dbe) {
            System.err.println("Caught an exception during " +
                "initialization or processing: " + dbe.toString());
            if (runner != null)
                runner.terminate();
        }
            System.exit(0);
    } // end main  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="simpletxn_init_java"></a>Method: SimpleTxn.init()</h3>
            </div>
          </div>
        </div>
        <p>
                        The <code class="methodname">SimpleTxn.init()</code>
                        method is used to open our environment handle.
                        For readers familiar with writing transactional
                        DB applications, there should be no surprises
                        here. However, we will be adding to this in later
                        chapters as we roll replication into this example.
                </p>
        <p>
        The only thing worth noting in this method here is that 
        we relax our transactional durability guarantee for this application.
        We do this because the application will eventually be replicated and
        so we don't need a high durability guarantee.
</p>
        <pre class="programlisting">    public int init(SimpleConfig config)
        throws DatabaseException
    {
        int ret = 0;
        simpleConfig = config;
        EnvironmentConfig envConfig = new EnvironmentConfig();
        envConfig.setErrorStream(System.err);
        envConfig.setErrorPrefix(SimpleConfig.progname);

        envConfig.setCacheSize(SimpleConfig.CACHESIZE);
        envConfig.setTxnNoSync(true);

        envConfig.setAllowCreate(true);
        envConfig.setRunRecovery(true);
        envConfig.setInitializeLocking(true);
        envConfig.setInitializeLogging(true);
        envConfig.setInitializeCache(true);
        envConfig.setTransactional(true);
        try {
            dbenv = new Environment(simpleConfig.getHome(), envConfig);
        } catch(FileNotFoundException e) {
            System.err.println("FileNotFound exception: " + e.toString());
            System.err.println(
                "Ensure that the environment directory is pre-created.");
            ret = 1;
        }

        return ret;
    }  </pre>
        <p>
        Finally, we present the <code class="methodname">SimpleTxn.terminate()</code>
        method here. All this does is close the environment handle. Again,
        there should be no surprises here, but we provide the
        implementation for the sake of completeness anyway.
</p>
        <pre class="programlisting">    public void terminate()
        throws DatabaseException
    {
            dbenv.close();
    }  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="doloop_java"></a>Method: SimpleTxn.doloop()</h3>
            </div>
          </div>
        </div>
        <p>
                        We now implement our application's
                        primary data processing method. This
                        method provides a command prompt at which the
                        user can enter a stock ticker value and a price for
                        that value. This information is then entered to the
                        database.
                    </p>
        <p>
                            To display the database, simply enter
                            <code class="literal">return</code> at the prompt.
                    </p>
        <p>
                        To begin, we declare a database pointer:
                    </p>
        <pre class="programlisting">    public int doloop()
        throws DatabaseException, , UnsupportedEncodingException
    {
        Database db = null;  </pre>
        <p>
                    Next, we begin the loop and we immediately open our
                    database if it has not already been opened. 
                </p>
        <pre class="programlisting">        for (;;)
        {
            if (db == null) {
                DatabaseConfig dbconf = new DatabaseConfig();
                dbconf.setType(DatabaseType.BTREE);
                dbconf.setAllowCreate(true);
                dbconf.setTransactional(true);

                try {
                    db = dbenv.openDatabase(null,           // Txn handle
                                    SimpleConfig.progname,  // db filename 
                                    null,                   // db name
                                    dbconf);
               } catch (FileNotFoundException fnfe) {
                    System.err.println("File not found exception" + 
                                        fnfe.toString());
                    // Get here only if the environment home directory
                    // somehow does not exist.
               }
            }  </pre>
        <p>
            Now we implement our command prompt. This is a simple and not
            very robust implementation of a command prompt.
            If the user enters the keywords <code class="literal">exit</code>
            or <code class="literal">quit</code>, the loop is exited and the
            application ends. If the user enters nothing and instead simply
            presses <code class="literal">return</code>, the entire contents of the
            database is displayed. We use our
            <code class="methodname">printStocks()</code> method to display the
            database. (That implementation is shown next in this chapter.)
        </p>
        <p>
           Notice that very little error checking is performed on the data
           entered at this prompt.  If the user fails to enter at least one 
            space in the value string, a simple help message is printed and
            the prompt is returned to the user. That is the only error
            checking performed here. In a real-world application,
            at a minimum the application would probably check to ensure
            that the price was in fact an integer or float value. 
            However, in order to keep this example code as simple as
            possible, we refrain from implementing a thorough user interface.
        </p>
        <pre class="programlisting">            BufferedReader stdin =
                new BufferedReader(new InputStreamReader(System.in));

            // listen for input, and add it to the database.
            System.out.print("QUOTESERVER&gt; ");
            System.out.flush();
            String nextline = null;
            try {
                nextline = stdin.readLine();
            } catch (IOException ioe) {
                System.err.println("Unable to get data from stdin");
                break;
            }
            String[] words = nextline.split("\\s");

            // A blank line causes the DB to be dumped to stdout.
            if (words.length == 0 ||
                (words.length == 1 &amp;&amp; words[0].length() == 0)) {
                try {
                    printStocks(db);
                } catch (DatabaseException e) {
                    System.err.println("Got db exception reading " +
                        "DB: " + e.toString());
                    break;
                }
                continue;
            }

            if (words.length == 1 &amp;&amp;
                (words[0].compareToIgnoreCase("quit") == 0 ||
                words[0].compareToIgnoreCase("exit") == 0)) {
                break;
            } else if (words.length != 2) {
                System.err.println("Format: TICKER VALUE");
                continue;
            }  </pre>
        <p>
                Now we assign data to the <code class="classname">DatabaseEntry</code> 
                classes that we will use to write the new information to the database.
            </p>
        <pre class="programlisting">            DatabaseEntry key =
                    new DatabaseEntry(words[0].getBytes("UTF-8"));
            DatabaseEntry data =
                    new DatabaseEntry(words[1].getBytes("UTF-8"));  </pre>
        <p>
                Having done that, we can write the new information to the
                database. Remember that because a transaction handle is not
                explicitly used, but we did open the database such that it
                supports transactions, then autocommit is automatically
                used for this database write.
            </p>
        <p>
                    Autocommit is described in the 
                    <em class="citetitle">Berkeley DB Getting Started with Transaction Processing</em> guide.
                </p>
        <p>
                Also, the database is not configured for duplicate records, so
                the data portion of a record is overwritten if the provided
                key already exists in the database. However, in this case
                DB returns <code class="methodname">OperationStatus.KEYEXIST</code> — which
                we ignore.
            </p>
        <pre class="programlisting">            db.put(null, key, data);  </pre>
        <p>
            Finally, we close our database before returning from the
            method.
        </p>
        <pre class="programlisting">        }
        if (db != null)
            db.close(true);
        return 0;
    }  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="printstocks_c"></a>
                            
                            
                            <span>Method: SimpleTxn.printStocks()</span>
                    </h3>
            </div>
          </div>
        </div>
        <p>
                        The  
                         <code class="methodname">printStocks()</code> 
                        
                        <span>method</span>
                        simply takes a database handle, opens a cursor, and uses 
                        it to display all the information it finds in a database.
                        This is trivial cursor operation that should hold
                        no surprises for you. We simply provide it here for
                        the sake of completeness.
                    </p>
        <p>
                        If you are unfamiliar with basic cursor operations,
                        please see the <em class="citetitle">Getting Started with Berkeley DB</em>
                        guide.
                    </p>
        <pre class="programlisting">    public void terminate()
        throws DatabaseException
    {
            dbenv.close();
    }

    /*
     * void return type since error conditions are propagated
     * via exceptions.
     */
    private void printStocks(Database db)
        throws DatabaseException
    {
        Cursor dbc = db.openCursor(null, null);

        System.out.println("\tSymbol\tPrice");
        System.out.println("\t======\t=====");

        DatabaseEntry key = new DatabaseEntry();
        DatabaseEntry data = new DatabaseEntry();
        OperationStatus ret;
        for (ret = dbc.getFirst(key, data, LockMode.DEFAULT);
            ret == OperationStatus.SUCCESS;
            ret = dbc.getNext(key, data, LockMode.DEFAULT)) {
            String keystr = new String
                (key.getData(), key.getOffset(), key.getSize());
            String datastr = new String
                (data.getData(), data.getOffset(), data.getSize());
            System.out.println("\t"+keystr+"\t"+datastr);

        }
        dbc.close();
    }
} // end class  </pre>
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